基于半嵌入结构的超透镜共聚焦特性

Confocal properties of metalens based on semi-embedded structure

摘要:

本文设计了一种1:1比例的半嵌入全介质超透镜,能够实现不同窄波段的共聚焦特性。采用时域有限差分法对不同高度和晶格常数下纳米单元的相移进行了数值分析。基于惠更斯-菲涅耳原理,构建了1环(半径为7.7 μm)和3环(半径为13.5 μm)的超透镜,并对比分析了它们的聚焦特性。在3环设计下,当波长为600 nm、线偏振光时,超透镜的焦距离设计目标偏差约为2.2%,焦点半高全宽为1.1 μm,聚焦效率达到68.28%。此外,还对650~490 nm波段内的超透镜色散进行了分析,并得到了650~550 nm波段内100 nm带宽和550~490 nm波段内60 nm带宽的恒定共聚焦焦点,这是由于焦深的存在所导致的。所设计的超透镜结构具有偏振不敏感、亚衍射极限聚焦、变焦和窄波段共聚焦的特性,在超分辨率、光路复用、彩色成像等领域具有潜在的应用价值。

Abstract:

In this paper, a 1:1 semi-embedded all-medium metalens is designed, which can realize confocal characteristics of different narrow bands. The finite difference time domain method was used to analyze the phase shift of nanocrystals at different heights and lattice constants. Based on Huygens-Fresnel principle, 1-ring (7.7μm radius) and 3-rings (13.5μm radius) metalens are constructed and their confocal properties are compared and analyzed. Under the 3-ring design, when the wavelength is 600 nm and the light is linearly polarized, the design target deviation of the focal distance of the metalens is about 2.2%, the full width at half maximum of the focal is 1.1μm, and the focusing efficiency reaches 68.28%. In addition, the dispersion of the metalens in the band 650~490 nm is analyzed, and a constant confocal focus of 100 nm bandwidth in the band 650~550 nm and 60 nm bandwidth in the band 550~490 nm is obtained, which is caused by the presence of focal depth. The designed metalens structure has the characteristics of polarization insensitivity, sub-diffraction-limited focusing, zoom and narrow band confocal, which has potential application value in the fields of super resolution, optical multiplexing and color imaging.